Electric protective device



April 25, 1939. A, ofl usg 2,156,058

ELECTRIC PROTECTIVE DEVICE Filed April 4, 1938 IIIIIIIIII 4, ,1 I'll fIIIIIIItifllllllllllllllflldlllIllllllIIIIIIIIIIIIIII'IIIII'IIIIIIIIIIII'llld1 W v IE4 Inventor: KarlA. Lohausen,

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Patented Apr. 25, 1939 UNITED STATES ELECTRIC PROTECTIVE DEVICE Karl A.Lohausen, Berlin-Oberschoneweide, Germany, assignor to General ElectricCompany, a corporation of New York Application April 4, 1938, Serial No.199,948 In Germany April 10, 1937 10 Claims.

The present invention relates to electric protective devices, moreparticularly of the type which operate on the expulsion principle, andhas for a principal object the provision of improvements in expulsionprotective devices whereby such devices may be designed for highercapacity ratings than heretofore considered practical while at the sametime making it possible to maintain the dimensions of such de- 10 viceswithin reasonable and practical limits.

In the design of expulsion protective devices, it has been found that,for interruption of currents of large magnitude, there is required astrong enclosing casing in order to withstand the high 15 pressuresdeveloped, and, also, a certain minimum and comparatively largecross-section of expulsion bore in order to prevent rise of thepressures beyond safe limits. n the other hand, it is required forsatisfactory interruption m of currents of small magnitude, that thecrosssection of the expulsion bore be as small as possible in order thatsuiilcient pressure may be developed for proper arc extinction.

The last two contradictory requirements, men- 25 tioned in the precedingparagraph, have presented a considerable problem in the design ofexpulsion protective devices and have constituted a major reason for thepresent comparatively re stricted scope of application of such devices,both 30 as regards pressure limits and current interrupting ability.Numerous proposals have been advanced for the solution of this diflicultproblem, among which has been that of providing, in expulsion fusedevices employing a single conductor enclosed in an expulsion bore ofrelatively large cross-section, an inner expulsion tube in surroundingrelation to the conductor, which inner tube has a relatively small boreand the walls of which are adapted to yield or rupture upon 40development of high pressures incident to interruption of largecurrents. However, in the practice of these proposals, limitations as tocurrent interrupting capacity, pressure limits and other factors havebeen encountered and, with 45 particular reference to the specificexample mentioned, there are presented certain important disadvantageswhich will be referred to hereinafter.

An important object of the present invention 50 is therefore theprovision of an improved expulsion safety device having increasedpressure limits and capacity for interruption of currents of largemagnitude, which at the same time is capable satisfactorily ofinterrupting currents of ll small magnitude.

Other objects and the details of that which I believe to be novel and mypresent invention will become apparent from the following descriptionand the claims appended thereto, taken in conjunction with theaccompanying drawing in 5 which are illustrated exemplary embodiments ofthe invention as applied to expulsion protective devices of the fusedtype. In the drawing, Figs.

1 and 2 show respectively longitudinal and transverse sections of oneform of expulsion fuse v device, and Figs. 3 and 4 show respectivelylongitudinal and transverse sections of a second form of expulsion fusedevice, embodying. the invention.

Each of the fuse devices illustrated has an insulating enclosing casingl0 provided with terminal elements II and I2, disposed respectively atopposite ends of the casing, between which are connected electrically inparallel a plurality of fusible conductors l3 disposed within thecasing. These conductors extend respectively through a plurality oftube-like expulsion chambers, one of which, designated M, is centrallylocated, and the others of which, designated l5, are arranged in acircle around the central chamber. The partition walls of the chambersare so dimensioned that, upon occurrence of an excess current of largemagnitude, such as due to shortcircuit or heavy overload, one, several,or all of the partitions open or burst so as to provide communicationbetween adjacent chambers. As a result of this, the arc gases,corresponding roughly in quantity developed to the current strength, canexpand in a space which is greater than that of a single chamber and, inan extreme case, can fill out a space corresponding to that of theaggregate of all of the chambers, so that rise in pressure within thecasing beyond a safe limit is avoided. Thus the several chambers ineffect combine with each other on heavy current inter- 4o ruption, dueto yielding of the separating walls or partitions, so that there isproduced a common are which is quenched by the expulsion of the gases,unhindered due to the effective enlargement of the expulsion bore, andat the same time the developed gas pressures are maintained withincontrollable limits.

In the embodiment of Figs. 1 and 2, one end of each of the fusibleconductors I3 is connected to terminal element H by solder, as indicatedat It, or other suitable means, while the other ends of the conductorsare connected in a similar manner, as indicated at IT, to a relativelythin and light conductive plate l8 which is releasably secured by asmall body of solder or other suitable means, as indicated at l9, so asto be readily expellable upon fuse operation. Adjacent ones of thechambers ii are separated from each other by radially inwardlyprojecting partitions or fins 20 which are integral with casing III.Casing l0 preferably is constructed of insulating material adapted forextrusion in the form illustrated, but may be constructed by any othersuitable process if desired. Chamber I4 is formed by an insulating tube2| disposed centrally of fins 20 and the walls of which abut the innerextremities of the fins. Although illustrated as being a separateelement, tube 2| may by suitable extrusion process be formed integrallywith casing l0 and the fins or partition walls 20. Preferably thecentral chamber has a slightly smaller effective cross-section than thatof the chambers I5, and the walls of tube 2| are slightly thinner thanpartitions 20. As a result of this expedient, upon large excesscurrents, a higher pressure initially is developed within chamber l4 sothat the walls of tube 2| burst, either in whole or in part, to placethe central chamber in communication with one or more of the chambersIS, The radially extending, relatively thick partition walls 20 thenextend into the gases to assist in the interruption process by provisionof an increased cooling effect. Preferably also partitions 20 are madeof a fibrous or other suitable insulating material which, under theaction of the arc, does not become electrically conductive, but producesarc quenching gases for aid in the arc extinction process, As analternative, any suitable and well known material having theseproperties may be applied as a coating to the partition walls.

In the modification of Figs. 3 and 4, the fusible conductors iii areconnected at one end to terminal element I I in the same manner, asindicated at l6, as that employed in the embodiment of Fig. 1, while theflexible braided extensions 25 of the other ends of the conductors aresecured directly to the inner wall of terminal I! by solder, asindicated at 26, or other suitable means. The conductors are surroundedrespectively by a plurality of relatively thin walled insulating tubes21 disposed within thick walled casing Ill and arranged, as best shownin Fig. 4, so as to provide a relation of chambers similar to that ofthe embodiment of Figs. 1 and 2. As in the previously describedembodiment, one or more of the individual chambers may be made to have aslightly smaller cross-section than that of the other chambers and thewalls of such smaller chamber or chambers may be made relatively thinnerso that bursting takes place initially with respect to the walls of thesmaller chamber or chambers. Also, tubes 21 may be constructed offibrous or other suitable insulating material which does not becomeelectrically conductive upon being subjected to the heat of an arc andwhich is capable of developing arc quenching gases, or a material havingthese desirable characteristics may be applied as a coating to the innerwalls of the tubes. Upon occurrence of large excess currents, such asdue to short-circuit or heavy overload, the operation is substantiallythe same as that of the embodiment previously described, in that one,several, or all of the tubes burst so as to provide intercommunicationbetween the individual chambers and the space within casing Ill, therebyaffording an effective enlargement of the expulsion bore for theexpansion of the developed gases therein so that dangerously exces-"characteristics of the different conductors, one

of them first attains fusing temperature and ruptures. The remainingparallel connected conductors then take over the whole current until asecond one of the conductors attains fusing temperature and ruptures.This operation continues progressively until the one of the conductorsfinally remaining carries the whole current. At this time theinterrupting process actually begins and is facilitated by the fact thatthe finally remaining conductor, though of small cross-section, hasimposed thereon the heavy duty of carrying the whole current so thatupon rupture thereof a gap is opened very rapidly. After the resultantarc burns the ruptured ends of this final conductor back a certaindistance, the arc transfers to one of the shorter gaps between the endsof one of the previously ruptured conductors and burns back these latterends. Thereupon the arc transfers to the gap of still another one of thepreviously ruptured conductors and this transfer of the are from chamberto chamber continues until all of the fusible conductors have beenburned back sufliciently to effect total interruption of the currentflow. Due to the small bores of the individual tubes and the progressivefusion of the individual conductors, the described devices are capablevery effectively and satisfactorily of interrupting extremely lowcurrents.

Between the operations described for extremely high and extremely lowcurrent interruption, various combinations of these operations takeplace to greater or less extent for interruption of intermediatecurrents, thereby insuring satisfactory operation over a wide range ofcurrent magnitudes.

Expulsion devices of the present invention afford distinct and importantadvantages over the 1 types of expulsion device, previously referred to,employing a single fusible conductor and a single inner enclosing tube.The total heat developed in the case of a plurality of parallelconnected fusible conductors is about the same as for a single fusibleconductor designed to carry the same current, since the total metal tobe vaporized is before interruption approximately the same in bothcases. In the operation of the devices of the present invention, thetotal heat due to arcing is distributed among the several chambers, anarc remaining only temporarily in any one of the chambers. Thus theconstruction of the herein described devices has the pronouncedadvantage that it considerably reduces the danger of detrimentalcarbonization of the enclosing walls which is experienced with thesingle conductor and single inner tube arrangements.

Also with expulsion fuse devices of the type hereinbefore referred to asemploying only a single conductor, the disadvantage is encountered thatupon interruption of extremely large currents, portions of the rupturedconductor are ejected at very high speed and in such manner as toendanger the safety of any one who may be located in the path of theejected portion. This disadvantage may be avoided effectively withexpulsion fuse devices constructed in accordance with the presentinvention, in that a relatively large number of parallel connected smallcrosssection conductors may be employed, thereby greatly reducing themass of any single conductor portion which may be ejected upon useoperation.

A still further advantage or the herein described construction over aconstruction, such as previously referred to, providing only a singlearcing path, is that the described construction, which provides aplurality of parallel arcing paths distributed among a plurality ofexpulsion chambers, permits the use of smaller bore tubes or enclosuresfor-the individual chambers. By this means more intimate contact of thearcs with the partition walls is secured, the interrupting time isshortened, low current interruption is made more positive, andmaterially improved overall operating characteristics are obtained.

As will be evident from the foregoing description my invention is notlimited to particular details of construction of the exemplaryembodiments illustrated, and I contemplate that various modificationswill suggest themselves to one skilled in the art. It is my intention,therefore, that the appended claims shall cover such modifications andother embodiments as do not depart from the true spirit and scope of thepresent invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In an electric protective device of the expulsion type, a tubularcasing of relatively strong construction having spaced terminalsassociated therewith, means providing in said casing a plurality ofsubstantially parallel extending expulsion chambers having wall portionsyieldable under high pressure, and means electrically in parallelarranged so as to produce arcs respectively in said chambers, saidchambers being operative to interrupt therein arcs of relatively lowcurrent magnitude, and said yieldable wall portions being operativeunder pressures incident to arcs of relatively large current magnitudeto ailord efiective enlargement of the arc gas expansion space.

2. In an electric protective device of the expulsion type, an enclosingexpulsion casing of relatively strong construction having spacedterminals associated therewith, partitioning means in said casingdefining a plurality of substantially parallel extending and relativelysmall bore expulsion chambers, and means electrically in parallelarranged so as to produce arcs respectively in said chambers, saidchambers being operative to effect interruption therein of arcs incidentto excess current of relatively small magnitude, and at least portionsof said partition means being constructed to yield so as to afiordcommunication between said chambers and adjacent spaces within saidcasing under the influence of high pressures incident to arcs producedby currents of relatively large magnitude.

3. In an electric protective device of the expulsion type, a relativelystrong enclosing expulsion casing having spaced terminals associatedtherewith, a plurality of conducting means, each including a fusiblesection, extending in said casing and connected electrically in parallelbetween said terminals, and partition means defining a plurality ofsubstantially parallel extending expulsion chambers respectivelyindividual to said conducting means, said chambers being operative tointerrupt therein arcs incident to relatively low current rupture ofsaid fusible sections, and at least portions of said partition meansbeing constructed to yield so as to aiford communication betweenadjacent spaces within said casing upon development of high pressures insaid chambers incident to rupture of said fusible sections by current ofrelatively large magnitude.

4. In an electric protective device of the expulsion type, a relativelystrong enclosing casing having spaced terminals, partition means in saidcasing defining a plurality of substantally parallel expulsion chambersoperative to interrupt therein arcs of relatively low current magnitudeand having wall portions constructed to yield under high pressuresincident to arcs of relatively high current magnitude, and meanselectrically in parallel arranged so as to produce arcs respectively insaid chambers, at least portions of the said partiiton means which formthe walls of certain of said chambers being of relatively weakerconstruction than other of the said partition means which form walls ofother of said chambers.

5. In an electric protective device of the expulsion type, a relativelystrong enclosing casing having spaced terminals, partition means in saidcasing defining a plurality of substantially parallel extendingexpulsion chambers operative to interrupt therein arcs of relatively lowcurrent magnitude and having wall portions constructed to yield underhigh pressures incident to arcs of relatively high current magnitude,and means electrically in parallel arranged so as to produce arcsrespectively in said chambers, certain of said chambers havingrelatively smaller cross-section than other of said chambers.

6. In an electric protective device of the expulsion type, a relativelystrong enclosing casing defining a plurality of substantially parallelextending expulsion chambers operative to interrupt therein arcs ofrelatively low current magnitude and having wall portions constructed toyield under high pressures incident to arcs of relatively high currentmagnitude, and means electrically in parallel arranged to produce arcsrespectively in said chambers, at least one of said chambers having arelatively smaller cross-section than other of said chambers and atleast a portion of the said partition means which form the walls of saidone chamber being of relatively weaker construction than other of thesaid partition means which form walls of said other of the chambers.

7. In an electric protective device of the expulsion type, a relativelystrong expulsion casing having spaced terminals, a plurality of tubesdisposed in substantially parallel extending relationship in said casingand arranged to provide expulsion chambers operative to interrupttherein arcs of relatively low current magnitude, and means electricallyin parallel arranged so as to produce arcs respectively in saidchambers, at least portions of the walls of said tubes being constructedto yield so as to afiord communication between said chambers andadjacent spaces with said casing upon development of high pres sures inthe chambers incident to arcs of relatively high current magnitude.

8. In an electric protective device of the expulsion type, a relativelystrong enclosing casing having spaced terminals, partition means in saidcasing defining a plurality of substantially parallel extendingexpulsion bores operative to interrupt therein arcs of relatively lowcurrent magnitude, at least one of said bores being locatedsubstantially centrally of said casing and others of said bores beinglocated around said central bore, and means electrically in parallelarranged so as to produce arcs respectively in said bores, at least aportion of said partition means being constructed to yield so as toafford eflective enlargement of the gas expansion space upon subjectionof said yieldable portion to high pressure incident to arcs ofrelatively larger current magnitude. v

9. In an electric protective device of the expulsion type, a relativelystrong tubular expulsion casing having spaced terminals, means providingpressure of predetermined magnitude so as to allord communicationbetween said chambers.

10. A housing for an electric protective device ,of the expulsion type,comprising a tubular expulsion casing of relatively strong construction,wall means defining an expulsion chamber extending substantiallylongitudinally and centrally of said casing, and means including aplurality of-partitions, extending substantially longitudinally of thecasing and projecting inwardly from the inner wall of the owing inspaced relationship, cooperative with said first mentioned means to forma plurality of expulsion chambers arranged around said flrst mentionedchamber, at least a portion of the walls separating said central chamberfrom the said chambers therearound being relatively weaker than saidpartitions and being yieldable under pressure of predetermined magnitudeso as to afford communication between said chambers.

KARL A. LOHAUSEN.

